Feedmarker is a free new service for social bookmarking of webpages and webfeeds.
I currently use Bloglines as my webfeed news reader, and del.icio.us for bookmarking. I have long wished that I could use the two services together, because both of them are extremely useful to me. Bloglines does have the ability to store or "blog" about a link, but what they offer is not social enough.
Feedmarker seems to solve those problems for me. Right now the service is young with few users, so the social part of the bookmarking is not really happening. But I'm sure del.icio.us was the same way in it's first month.